The invention relates to the production of medicaments, and especially of neuroprotective and retinoprotective medicaments (or drugs) for the prevention and/or the treatment of ophthalmologic conditions leading to damage to the retina and to the optic nerve, which result in a loss of vision (especially far and near visual acuity, contrast vision, color vision and/or visual field). These medicaments comprise at least one active principle which is a leucine, for example, the N-acetyl-DL-leucine. This leucine can be associated with other active principles and, in particular, with Ramipril or Ramiprilate.
The invention especially aims to provide medicaments intended for the prevention and/or the treatment of ophthalmologic diseases or disorders, which can improve visual function, in particular, far and/or near visual acuity, contrast vision, color vision and/or visual field, in patients suffering from chorioretinal and/or optic nerve diseases. Examples of such diseases or disorders that can be mentioned are:                hereditary dystrophies of the retina, for example, pigmentosa retinopathy or stargardt's disease;        glaucomatous neuropathy and more generally glaucoma;        age-related macular degeneration (ARMD) and myopic macular degeneration.        
The invention also aims to provide medicaments intended for the prevention and/or the treatment of visual refractive disorders, especially myopia, hypermetropia, presbyopia, astigmatism, and for stabilizing and improving vision in patients that have such visual refractive disorders.
The medicaments according to the invention are not limited to the above-mentioned uses. They can be used efficiently in preventing or slowing down, or even stopping, the age-related “natural” decreases in visual acuity or visual field or both at the same time.
Indeed, mean retinal sensitivity reduces linearly with age. This decline starts very early on, from 20 years of age, and accelerates after the age of 60.
In particular, the mean sensitivity (MS) expressed in decibels (dB) obeys the following equation, according to Jaffe: MS (dB)=28.8−0.074×age.
As shown in the examples, administration of N-acetyl-DL-leucine to patients via the systemic route (especially in an oral or injectable form) or the topical route (especially in the form of eye drops, an ointment or a cream) improved visual acuity, contrast vision, color vision but also visual field.
The N-acetyl-DL-leucine (C8H15NO3) is a small molecule, with a relatively simple chemical structure. This optically inactive product is the result of N-acetylation of α-amino-isocaproic acid (C6H13NO2), the L isomer of which, leucine, is a widespread natural α-amino acid.
Leucine:

The N-acetyl-DL-leucine has the following formula:

The effect of N-acetyl-DL-leucine on experimental vertigo in mice was discovered in 1957. Since this date, this compound is used successfully in human clinical medicine as a symptomatic medicament in vertigo states.
The N-acetyl-DL-leucine is widely prescribed by the doctors, well known from the pharmacists under the name Tanganil® (Pierre Fabre Medicament), and its efficiency is appreciated from many patients suffering from vertigo. However, the mechanism of action of this medicament is still subject to controversy.
The N-acetyl-DL-leucine was first disclosed by Emil Ficher, a very famous Professor of Chemistry at the University of Berlin, whose work in biochimistry and biological organic chemistry was rewarded by the Nobel Prize for Chemistry in 1902. The year before, in 1901, he published the preparation of the racemic acetyl derivative of leucine, obtained by reacting a solution of acetic anhydride in acetic acid with the amino acid ester.
Although the N-acetyl-DL-leucine has a favorable effect on vertigo, its potential for ophthalmologic applications was unknown before the present invention was made.
As disclosed herein, in the examples, observations based on real assays were made in patients having a glaucomatous neuropathy or a glaucoma, a hereditary dystrophy of the retina (for example, pigmentosa retinopathy or stargardt's disease), macular degeneration, myopia, hypermetropia, presbyopia or astigmatism, hemeralopia or a age-related physiologic loss of vision.
Hence, the invention relates to the use of a leucine and especially of the N-acetyl-DL-leucine, for the manufacture of medicaments intended for improving visual acuity and/or visual field in treated patients.